The present invention relates to the field of microelectronic device manufacture, and more particularly relates to methods and apparatus suitable for encapsulating microelectronic subassemblies such as semiconductor chip subassemblies.
For example, as described in commonly assigned U.S. Pat. Nos. 5,148,266; 5,148,265; 5,258,330 and 5,398,863, certain microelectronic subassemblies may incorporate a microelectronic element such as a semiconductor chip, a dielectric layer such as a flexible, sheet-like dielectric with terminals thereon connected to the microelectronic element or semiconductor chip and a layer of a compliant material disposed between the dielectric layer and the semiconductor or microelectronic element. Such compliant layer can be formed, in whole or in part, by injecting a curable liquid material between the dielectric and the chip or microelectronic element. The curable liquid encapsulant may also serve to encapsulate the flexible leads. Specific methods for introducing encapsulant are disclosed in co-pending, commonly assigned U.S. Pat. No. 08/123,882, filed Sep. 20, 1993; 08/246,113, filed May 19, 1994 and 08/366,236 filed Dec. 28, 1994. As further described in co-pending, commonly assigned U.S. Pat. No. 08/271,768, filed Jul. 7, 1994, the microelectronic assembly may be fabricated by connecting leads between the terminals on the dielectric element and the microelectronic element and then moving the dielectric element and microelectronic element relative to one another to thereby deform the leads. Assemblies of this type may also be provided with a compliant layer by injection of a liquid encapsulant between the dielectric layer and the microelectronic element.
A further process for encapsulation of microelectronic elements is taught in U.S. Pat. No. 4,374,080. In this process, the devices to be encapsulated are disposed in mold cavities which are filled with a fine, powder filler through a filling orifice initially disposed at the top of the cavity. After addition of the filler, the cavities are inverted to drain off excess powder filler while still leaving some powder filler in the mold cavities surrounding the device. Following this, the liquid encapsulant is added and a vacuum is drawn so that gases trapped in the molding cavity, between the particles of filler, bubble up through the encapsulant. After degassing, the encapsulant is cured.
Other methods of encapsulation include transfer molding and injection molding. In these methods, the subassembly is positioned within a mold cavity and the encapsulating material is forced into the cavity around the subassembly. If the encapsulant is an elastomer which requires substantial curing time, each subassembly must remain in the mold for a prolonged period. Consequently, productivity of these methods is limited. In a "glob-top" encapsulation process, the encapsulant is applied over the chip and the surrounding region of the substrate without a mold. The glob-top process cannot be used with certain types of assemblies.
Despite these and other efforts in the art, there has been need for further development of encapsulation fixtures and methods. In particular, further improvement in encapsulation fixtures and methods capable of processing numerous semiconductor devices would be desirable. There are particular needs for fixtures and methods which are usable with encapsulants such as elastomers having long cure times.